Chapter 16- Gene Regulation in Prokaryotes

Trans Acting

Able to control the expression of genes on other DNA molecules

Cis Acting

Able to control the expression of genes only when on the same piece of DNA

Permease

Actively transports lactose into the cell

Attenuation

Affects the continuation of transcription, not its initiation This action terminates the translation before it reaches the structural genes (Product for attenuation is always an amino acid)

CAP

Binds in front of the promoter which recruits polymerase and in turn boosts the transcription of the region, turns on lac and other operons

Promoter Mutations

Cis Acting, Interferes with the binding of RNA polymerase to the promoter Do not produce lac proteins with or without the presence of lactose

Constitutive Expression

Continuously expressed under normal cellular conditions

Regulator Gene

DNA sequence encoding products that affect the operon function, but aren't part of the operon

Hungry Cell?

Depends on glucose levels

Lac Z

Encodes B- Galactosidase

Lac Y

Encodes Permerase

Lac X

Encodes Transacetylase

Negative Control

Inhibit gene expression

Structural Genes

Lac Z Lac Y Lac X

Glucose is Low

Levels of cAMP are high, binds to CAP, and this complex binds to DNA Increases the efficiency of polymerase binding on the lac operon Results in high rates of transcription and translation of structural genes, producing glucose

Glucose is High

Levels of cAMP are low, and cAMP is less likely to bind to CAP RNA polymerase does not bind to DNA as effectively

Regulator Gene Mutations

Mutations of the LacI gene affect both the production of B-Galactosidase and permerase because genes for both proteins are on the same operon and are regulated coordinately.

SuperRepressors

Produced a repressor with an altered inducer-binding site, which prevented the inducer from binding to the repressor, translation was always prevented. Shuts down pathway with or without lactose Dominant

Lac P

Promoter

Operon

Promoter and additional sequences that control transcription (operator) and structure of genes

High Tryptophan Levels

Region 1 binds to region 2, which leads to the binding of region 3 and region 4, terminating transcription prematurely.

Low Tryptophan Levels

Region 2 binds to region 3, which prevents the binding of region 3 and region 4, and transcription continues.

Lac I

Regulator Gene which creates a repressor Active regulator protein (repressor), binds to the operator Allosteric regulation

Operator Mutations

Repressor protein was no longer able to bind Dominant Cis Acting

When Lactose is Present

Repressor will not bind to the operator- let transcription and translation occur Lactose is converted in to Allolactose which binds to the repressor and via allosteric regulation prevents it from binding to the operator

Positive Control

Stimulate gene expression

Structural Gene Mutations

Structure of the proteins was affected. Mapped to Lac Z and Y. These we're independent and usually only affected the product of the gene in which they occurred.

Partial Diploid

Two different DNA molecules: the full bacterial chromosome and an extra piece of DNA

Regulation

mRNA processing Stability Translation Postmodification (active protein) Primarily regulated by being transcribed or not being transcribed.